Are you sure it is every 15 minutes? I created an event 36 minutes ago which should have caused a trigger but nothing happened.
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user18015Mar 10 '12 at 21:48

Seems to take a little longer sometimes. I bet 15 minutes is an average or an estimate.
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Travis PflanzMay 8 '12 at 4:29

2

The answer above is wrong. SMS (texting your IFTTT number) takes only 4 seconds to trigger. Phone (calling your IFTTT number) takes 4 seconds to trigger. Date and Time (IFTTT clock) is accurate down to the minute. For those interested in the wrong answer see above. For those interested in the correct answer see: How long is the delay between ifttt trigger and posting action?
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Aaron KlapMay 22 '14 at 2:26

anyone who has actually used their service will know this is obviously wrong in many cases. Here is what I have found for the time it takes for the trigger to initiate the task:

SMS (texting your IFTTT number) - 4 seconds, nearly instant.

Twitter - 10 minutes to 15 minutes.

Phone (calling your IFTTT number) - 4 seconds, nearly instant.

Date and Time (IFTTT clock) - accurate down to the minute.

Feel free to add to this list over time.

15 minutes = 900 seconds. Percent error = (stated value - actual value) / actual value * 100%. If you relied on the value of 15 minutes for the phone response time then the percent error would be (900-4)/4*100% = 22,400%. 22,400% error is a very large error! The 15 minute response time can be very inaccurate.

I noticed that after a month, an android trigger occurred, but the IFTTT site listed it as not occurring. This has happened to me for two recipes involving my android phone. How I solved this was to uninstall the IFTTT app on my android phone, then remove the android channel, then install the IFTTT application on my android phone again, and activate the channel. After performing these steps the triggers started "triggering" again.

SMS & Phone definitely don't work like that anymore... unless it's the newness of the account, the recipe, or the channel activation that's making them take their time (I just set up everything just today). I've been waiting over an hour for text & voicemail alerts to automatically trigger, though if I manually hit the "Refresh" button on the recipe itself the text (sent over 30 minutes ago) will generate the desired action. I haven't yet seen it automatically trigger based on a phone call or a text message.
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Brad BeyenhofOct 31 '14 at 18:43

Tasks do poll for trigger data every 15 minutesofficially, but there's some nuance to this that might be helpful to people who don't work with web services.

Polling means requesting new info periodically.

Every IFTTT recipe has two sides - the If This (trigger) side, and the Then That
(action) side.

The trigger represents the search for something to
trigger the recipe.

The action represents what IFTTT does in response to the trigger.

Polling every 15 minutes means that the
trigger data will be checked that often, but says nothing about the
action time, which starts nearly immediately (although I expect
actions get queued to manage server load)